I would like to add that while you can use these healthier substitutes to calm a sweet tooth, that moderation is the key. If you are eating a low calorie diet-say 1400 calories a day, you do not want 400 calories of it to be "low fat junk". If you limit yourself to one low fat/low sugar/low carb (depending on what type of plan you are on) "treat", then limit it to one serving a day-maybe at snacktime.
The thing that is a big problem here in America especially, is that we have evolved to having cakes, cookies, and chips as a regular part of our daily diets-instead of for special occasions like birthdays and holidays. They are supposed to be "treats" and not a regular daily part of the diet. Healthy "real" foods should be eaten most of the time.
What I get a lot of here at 3FC is private messages asking "What am I doing wrong?" when someone hits a plateau, and a lot of time there are 3-4 diet treat foods eaten per day, even if the person is staying within their calorie, fat, WW points, or carb limits for their particular plan. What really helps is to have the occasional treat, but to make it just that-a treat.
There are some fabulous diet friendly treats that are actually a truly healthy choice-if you like apple pie, core an apple, put some cinnamon and a dash of Splenda in the center cored out area, and microwave it 30 seconds at a time (checking it for doneness) until it is cooked through. MARVELOUS...and 100% fruit.
I am absolutely not saying that you shouldn't eat diet treats-but there are a lot of dieters eating very little or no fruits and veggies-but having 2-3 Skinny Cows a day.